Bionomics of the Pine Needle Scale, Chionaspis pinifoliae,1, 2 and Its Natural Enemies at South Lake Tahoe, Calif.3

Abstract

A study of the life histories of the pine needle scale, Chionaspis (Phenacaspis) pinifoliae (Fitch) and its natural enemies was undertaken at South Lake Tahoe, Calif., to provide a basis for a study of its population dynamics. Two distinct scale populations occur sympatrically, one on lodgepole pine (Pinus contorta) and one on Jeffrey pine (P. jeffreyi). The lodgepole pine population is parthenogenetic and overwinters as eggs. The Jeffrey pine population is bisexual and overwinters as gravid females. The question remains unresolved as to whether distinct species or merely ecotypes are involved. The natural enemies associated with the scale consist of 3 endoparasitic chalcidoids, Prospaltella bella Gahan, Physcus howardi Compere and Achrysocharis phenacapsia Yoshimoto, and two predatory coccinellids, Chilocorus orbus Casey var. monticolus Drea and Cryptoweisia atronitens (Casey). The lodgepole pine scale is parasitized by P. bella and P. howardi. The Jeffrey pine scale is parasitized by A. phenacapsia. These differences persist in mixed stands as well. P. bella and A. phenacapsia show strong synchrony and association with their host; P. howardi is less so. P. bella is arrhenotokus, and P. howardi and A. phenacapsia are thelytokus. C. atronitens ' life cycle requires a scale whose phenology is similar to C. pinifoliae. C. o. monticolus is apparently a more general feeder.